Searching for super-WIMPs in leptonic heavy meson decays

We study constraints on the models of bosonic super-weakly interacting particle (super-WIMP) dark matter (DM) with DM masses $m_X \sim $\mathcal{O}$(1 - 100)$keVfromleptonicdecays$M\rightarrow \ell \bar{\nu}_\ell + X$,where$M=B^\pm, D^\pm, D_s^\pm$isaheavymesonstate\mathrm{.}Wefocusontwocaseswhere$X$ denotes either a light pseudoscalar (axion-like), or a light vector state that couples to the standard model (SM) through kinetic mixing. We note that for a small DM mass these decays are separately sensitive to DM couplings to quarks, but not its mass.